Regional Gardening Reports :: National Gardening Association

In the Garden:
Western Mountains and High Plains
June, 2011
Regional Report

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To ensure prolific flowering, lilacs need periodic pruning.

Renewing Tired Lilacs

Lilacs are among my favorite spring-blooming shrubs and they are among the most rugged for our region. Just last month, my oldest son asked what kind of flowering shrub to plant in a hot, sunny west-facing exposure. Considering his gardening experience I recommended the common purple lilac. He took my advice, took his time to select a nice specimen and planted it earlier this year. It is doing very well and he's brimming with pride.

Lilacs often decrease in vigor and flowering as the shrubs mature and conditions within your landscape change. If the decline is not caused by a late freeze, the lack of sufficient sunlight, or poor air circulation around the plants, a hard renewal pruning may be what's needed. The best time to get this project underway is right after blooming finishes.

Renewal pruning of older lilac shrubs can help to solve some major causes for bloom decline. The process consists of removing the oldest, thickest canes at ground level. Often, these stems are infested with scale insects and borers. The thinning process will also eliminate some of the shading from overgrown stems and excess foliage.

New, young canes will have more light and air circulation, enabling them to grow and produce more vigorous blooms. I like to remove at least one third of the oldest canes yearly. This procedure will maintain the lilac without drastic measures and it will renew bloom in following years. Please, don't do the "tip pruning" method, which does not encourage more blooms but destroys the natural shape of the lilac shrub.

Some of the lilacs at the old farmstead residence have grown to eighteen feet or more. These too can be rejuvenated and coaxed to bloom more prolifically. Drastic measures will be needed and a sharp pruning saw or chainsaw. One-third to one half of the older stems should be cut down to within four or six inches above the ground. Next year, remove the remaining oldest canes. While this very hard pruning may seem severe and damaging, lilacs are resilient and will send out new, vigorous stems the first season after pruning to grow several feet. Within three years, these new canes will be ready for flowering.

If your lilac is lagging behind in blooms and it's been awhile since it had a good pruning, now is the time to get out the loppers and pruning saw, before next year's flower buds are set in July.

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